Multi-stage gearbox

ABSTRACT

A multi-stage gearbox with a drive input shaft connected to a reduction planetary gear set, with a drive output shaft connected to a main planetary gear set, and with shift elements. An input speed of the drive input shaft can be transferred, by the engagement of at least seven forward gears to the drive output shaft, in such manner that to shift from one gear to the next-higher or next-lower gear, only one shift element is disengaged and another shift element is engaged. The reduction planetary gear set has an output shaft rotating at an output speed of the reduction planetary gear set. The main planetary gear set is connected to the drive input shaft. The main planetary gear set is connected to the output shaft of the reduction planetary gear set.

This application is a national stage completion of PCT/EP02/03438 filedMar. 27, 2002 which claims priority from German Application Serial No.101 15 985.4 filed Mar. 30, 2001.

FIELD OF THE INVENTION

The present invention concerns a multi-stage gearbox.

BACKGROUND OF THE INVENTION

In the older German Patent Application No. DE 199 49 507 A1 by thepresent applicant several gearbox designs for an automatic multi-stagegearbox with various combinations of coupled planetary gear sets aredescribed. By a suitable connection of a non-shifting reductionplanetary gear set combination to a shiftable main planetary gear setcombination, at least seven respective forward gears can be engagedwithout range-change. The number of engageable forward gears is here atleast two more than the number of shift elements. The reduction and mainplanetary gear sets are in this case always arranged coaxially with oneanother.

For the above case DE 199 49 507 A1 proposes that the shiftable mainplanetary gear set combination be made as a two-web/four-shafttransmission with two shiftable main planetary gear sets. Here,two-web/four-shaft transmission is understood to mean an arrangement oftwo individual mechanically coupled one-web planetary gear sets, inwhich the coupled unit has four so-termed “free shafts” owing toduplicated component connection, where a “shaft” can be a solargearwheel, an annular gearwheel or even a web of a planetary gearwheelassembly.

Starting from the said state of the art, the purpose of the presentinvention is to provide a multi-stage gearbox with a non-coaxialarrangement of the drive input and drive output shafts and at leastseven forward gears that can be engaged without range-change, developedfurther in relation to structural volume, with comparatively lowconstruction cost, suitable gear ratio steps and a larger spread.

SUMMARY OF THE INVENTION

Beginning from the prior art of DE 199 49 507 A1 the multi-stage gearboxcomprises a reduction planetary gear set connected to the drive inputshaft of the transmission and a main planetary gear set connected to thedrive output shaft of the transmission, as well as several shiftelements.

In this, the reduction planetary gear set is preferably made as atwo-web/four shaft transmission with two coupled, shiftable reductionplanetary gear sets or with two coupled, non-shiftable reductionplanetary gear sets or with two mutually independent reduction planetarygear sets, one shiftable and the other not. Here, “independent” meansthat each of the two reduction planetary gear sets produces a rotationspeed which is unaffected by any active connection between the tworeduction planetary gear sets. The output speed of the reductionplanetary gear set is in this case, therefore, produced either by thefirst or by the second reduction planetary gear set, but not by both atthe same time.

The main planetary gear set is preferably made as a two-web/four shafttransmission with two coupled, shiftable main planetary gearwheelassemblies.

Obviously, other designs of the reduction and main planetary gear setscan be provided, for example, with fewer or more coupled planetary gearsets, with any desired number of component couplings within thereduction and main planetary gear sets and with fixed spur gear stagesinstead of planetary gearwheel assemblies in the reduction planetarygear set and/or the main planetary gear set.

According to the invention, the main planetary gear set can always beconnected, via at least one shift element, to the drive input shaft ofthe gearbox and is always connected, via a non-shiftable mechanicalconnection, to the output of the reduction planetary gear set.

According to the invention, it is proposed that this non-shiftablemechanical connection between the reduction planetary gear set and themain planetary gear set, and the coupling of the main planetary gear setto the drive shaft, should be made as a spur gear or as a bevel gear oras a hypoid gear. In a particularly advantageous way, this structureenables compact, space-saving arrangements of the reduction and mainplanetary gear sets of the multi-stage gearbox for applications withnon-coaxial drive input and output. The multi-stage gearbox constructedin this way, according to the invention, is particularly suitable formotor vehicles whose drive motor is arranged transversely to the drivingdirection (“front transverse drive”, “rear transverse drive”) or withthe drive motor arranged longitudinally to the driving direction andfront or rear drive.

By the selective shifting of shift elements that act on the reductionplanetary gear set or by the component structure of the reductionplanetary gear set and its connection to the drive input shaft of thegearbox, at the output of the reduction planetary gear set a certainrotation speed is produced at which the connecting shaft rotates, i.e.,a spur gear pair or a bevel gear pair or a hypoid gear pair.

Each gear is engaged by means of at least two shift elements. Whenshifting from one gear to the next, only one shift element is disengagedand one other shift element is engaged, so thatshifting-quality-critical, range-change shifts in which several shiftelements have to be engaged or disengaged at the same time, are avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIGS. 1A and 1B are a first embodiment of a multi-stage gearbox with aspur gear coupling between the reduction and main planetary gear setsaccording to the presently claimed invention;.

FIG. 2A is a second embodiment of a multi-stage gearbox with a spur gearcoupling between the reduction and main planetary gear sets according tothe presently claimed invention; and.

FIG. 3A third embodiment of a multi-stage gearbox with a bevel gearcoupling between the reduction and main planetary gear sets according tothe presently claimed invention.

DETAILED DESCRIPTION OF THE INVENTION

Corresponding to the respective embodiment, FIG. 1A shows a shift schemeof a multi-stage gearbox. FIG. 1B shows a shift logic pertaining to theembodiment, for example, a transmission ratio of individual gears, gearsteps, transmission spread and constant ratio of an individual planetarygear sets.

To provide multi-stage gearboxes with at least seven forward gears thatcan be manufactured comparatively inexpensively relative to DE 199 49507 A1, the reduction planetary gear set combination on the drive inputshaft of the gearbox is made shiftable. By virtue of this arrangement, afurther speed is produced in accordance with the shift elementsactuated, which acts on the shiftably designed main planetary gear setcombination on the drive output shaft, in addition to the input speedtransmitted by the drive input shaft. In accordance with the actuationlogic of the shift elements, the reduction planetary gear set can alsobe optionally blocked or fixed.

In the known multi-stage gearboxes described at the start, twoadditional speeds are produced by the reduction planetary gear setconnected to the drive input shaft which, together with the drive inputspeed, act upon the main planetary gear set. In contrast to the presentinvention, these two speeds are produced by virtue of the arrangement oftwo non-shiftable reduction planetary gearwheel assemblies.

By actuating the shift elements in the present invention, the outputspeed of the reduction planetary gear set combination and the gearboxinput speed are thus transferred to the drive output shaft in accordancewith the force flow engaged. Owing to the particular arrangement of theshift elements and planetary gear sets, various multi-stage gearboxeswith at least seven forward gears can be designed. Below is an exampleembodiment of the invention consisting of a nine-gear gearbox with atotal of six shift elements and four planetary gear sets described indetail.

As already mentioned, other designs of the reduction and main planetarygear sets and a different number and different connections of the shiftelements can obviously be provided.

In all the Figures, a drive input shaft of the gearbox is indexed 1 anda drive output shaft of the multi-stage transmission is indexed 3. Inall cases, the multi-stage gearbox in all cases has a shiftablereduction planetary gear set VS and a shiftable main planetary gear setNS connected to an output shaft 2 of the reduction planetary gear setVS. The drive input shaft 1 rotates at an input speed n. When two shiftelements of the reduction planetary gear set VS are engaged, i.e.,closed in accordance with the shift logic of the gearbox, the outputshaft 2 of the reduction planetary gear set VS rotates at an outputspeed nvs. The drive output shaft 3 rotates at an output speed nns ofthe main planetary gear set NS. VS1 and VS2 denote a first and secondreduction planetary gearwheel assembly, and NS1 and NS2 denote a firstand second main planetary gearwheel assembly. The gear set concept,i.e., the component-related coupling of the planetary gearwheel assemblycomponents, is identical in the example embodiments illustrated. Alsoidentical is the number and connection of the shift elements to theindividual planetary gearwheel assembly components. Three shift elementsA, B and D acting on a reduction planetary gear set VS and three shiftelements M, H and L acting on a main planetary gear set NS are provided.

FIG. 1A now shows the gearbox scheme of a first example embodiment of amulti-stage gearbox, according to the invention, with two shiftablereduction planetary gearwheel assemblies VS1, VS2 and three shiftelements A, B, D coupled to form a two-web, four shaft transmission unitconstituting the reduction planetary gear set VS, and two shiftable mainplanetary gearwheel assemblies NS1, NS2 and three shift elements M, H, Lcoupled to form a two-web, four shaft transmission unit constituting themain planetary gear set NS. According to the invention, the reductionand main planetary gear sets VS and NS are connected by a spur geararrangement ST such that the said arrangement ST comprises two spur gearstages. The first spur gear stage has a spur gearwheel ST11 on an inputside and a spur gearwheel ST12 on an output side, and connects the driveinput shaft 1 with a free shaft of the main planetary gear set NS, inthis case to a central gearwheel of the first main planetary gearwheelassembly NS1. Analogously to the nomenclature of the first spur gearstage, a second spur gear stage comprises a spur gearwheels ST21 (inputside) and a ST22 (output side) and connects the output shaft 2 of thereduction planetary gear set VS to another free shaft of the mainplanetary gear set NS, in this case, to a central gearwheel of thesecond main planetary gearwheel assembly NS2.

As shown in FIG. 1A, all four planetary gearwheel assemblies VS1, VS2,NS1 and NS2 are formed as minus-gears, each with a solar gearwheel 11,21, 31 and 41, an annular gearwheel 13, 23, 33 and 43 and a web 15, 25,35 and 45 with planetary gearwheels 12, 22, 32 and 42.

The solar gearwheel 11 of the first reduction planetary gearwheelassembly VS1 can be fixed by the first shift element A of the reductionplanetary gear set VS, which is formed as a brake. The solar gearwheel21 of the second shiftable reduction planetary gearwheel assembly VS2 isconnected fast to the drive input shaft 1 (rotation speed n). The web 15of the first reduction planetary gearwheel assembly VS1 and the annulargearwheel 23 of the second reduction planetary gearwheel assembly VS2are coupled and can be fixed by the second shift element B of thereduction planetary gear set VS, which is formed as a brake. The annulargearwheel 13 of the first reduction planetary gearwheel assembly VS1 andthe web 25 of the second reduction planetary gearwheel assembly VS2 arecoupled and can be fixed by the third shift element D of the reductionplanetary gear set VS, which is formed as a brake. The annular gearwheel23 of the second reduction planetary gearwheel assembly VS2 and thecoupled web 15 of the first reduction planetary gearwheel assembly VS1,at the same time, form the drive output of the reduction planetary gearset VS and are correspondingly connected to its output shaft 2 (rotationspeed nvs).

According to the invention, the drive input shaft 1 is connected fast toa spur gearwheel ST11 of the first spur gear stage ST11/ST12, and theoutput shaft 2 of the reduction planetary gear set VS is connected fastto the spur gearwheel ST21 of the second spur gear stage ST21/ST22 ofthe spur gear arrangement ST. The spur gearwheel ST12 which meshes withthe spur gearwheel ST11 can be connected with the solar gearwheel 31 ofthe first main planetary gearwheel assembly NS1 by means of the firstshift element M of the main planetary gear set NS, which is made as aclutch, and by means of the second shift element H of the main planetarygear set NS, also made as a clutch, with the annular gearwheel 33 of thefirst main planetary gearwheel assembly NS1 and the web 45 of the secondmain planetary gearwheel assembly NS2 coupled to the annular gearwheel33. A spur gearwheel ST22 which meshes with a spur gearwheel ST21 isconnected fast to the solar gearwheel 41 of the second main planetarygearwheel assembly NS2.

The reduction and main planetary gear sets VS and NS are arranged withparallel axes axially next to one another, with an offset between theircentral axes. According to the invention, the spur gear arrangement STis arranged axially between the reduction and main planetary gear setsVS and NS.

The web 45 of the second main planetary gearwheel assembly NS2 and theannular gearwheel 33 of the first main planetary gearwheel assembly NS1coupled to the web 45 can be fixed by means of the third shift element Lof the main planetary gear set NS, which is made as a brake. The annulargearwheel 43 of the second main planetary gearwheel assembly NS2 and theweb 35 of the first main planetary gearwheel assembly are coupled,forming the output drive of the main planetary gear set NS (rotationspeed nns) and being connected to the drive output shaft 3 of thegearbox.

In the example embodiment, according to FIG. 1A, both spur gear stagesST11/ST12 and ST21/ST22 have a transmission ratio of “one”. Obviously,in other embodiments of a multi-stage gearbox according to theinvention, other transmission ratios could be provided. The spur gearstages ST11/ST12 and ST21/ST22 could also have different transmissionratios or even more than two spur gearwheels in each spur gear stage orindeed a different number of spur gearwheels in each spur gear stage.

For the speeds of the shifts and shift elements, the following can besaid concerning the first embodiment of a multi-stage gearbox accordingto the invention:

-   1. The transmission ratio of the two spur gear stages ST11/ST12 and    ST21/ST22 is “one”.-   2. The speeds of the drive input shaft 1 and of shift element H are    equal (input speed n).-   3. The speed of the engaged shift element A is “zero”.-   4. The speed of the engaged shift element B is “zero”.-   5. The speed of the engaged shift element D is “zero”.-   6. The speed of the engaged shift element L is “zero”.-   7. When shift elements H and M are engaged, the speed of the central    gearwheel of the second main planetary gearwheel assembly NS2    connected to the output shaft 2 is equal to or greater than a speed    nvs produced by the reduction planetary gear set VS.-   8. When shift elements A and D are engaged, the speed of the shaft    which connects shift element B with a central gearwheel of the    second reduction planetary gearwheel assembly VS2, is smaller than    or equal to the speed produced when shift element B is actuated.-   9. When shift element A is engaged, the speed of the shaft    connecting shift element B to the central gearwheel of the second    reduction planetary gearwheel assembly VS2 is greater than or equal    to the speed produced when shift element B is actuated.-   10. The speed of shift element M when engaged is larger than zero    and smaller than or equal to the input speed n of the drive input    shaft 1, and-   11. When shift elements L and M are engaged, the speed of the    central gearwheel of the second main planetary gearwheel assembly    NS2 connected to the output shaft 2 is smaller than or equal to the    speed nvs produced by the reduction planetary gear set VS.

With the arrangement of FIG. 1A by selective closing of the six shiftelements, the nine forward gears and one reverse gear listed in thetable of FIG. 1B can be engaged without range-change, in very harmonioussteps and with a large spread. In this, three of the forward gears aredesigned as drive input speed reducing, overdrive gears.

Advantageously, four of the six shift elements are made as brakes withcorrespondingly favorable constructive effort, particularly in relationto their pressure oil supply. The coupling of the reduction and mainplanetary gear sets, via a fixed spur gear stage, according to theinvention, enables very compact, multiple-gear multi-stage gearboxes andis particularly appropriate for applications in motor vehicles withdrive motors arranged transversely to the driving direction (“fronttransverse drive” or “rear transverse drive”). In this, the offsetarrangement of the drive input and output shafts of the gearbox make itpossible to use spur gearwheels of relatively small diameter.

FIG. 2A shows the transmission scheme of a second example embodiment ofa multi-stage gearbox according to the invention. In contrast to thefirst embodiment described above, the reduction and main planetary gearsets VS and NS are arranged axis-parallel and in one plane. The spurgear stage ST that connects the reduction and main planetary gear setsVS and NS is now arranged axially adjacent to the reduction and mainplanetary gear sets VS and NS. The drive output shaft 3 of the gearboxis again axis-parallel to the drive input shaft 1.

The design of the reduction planetary gear set VS with two shiftablereduction planetary gearwheel assemblies VS1, VS2 coupled as two-web,four-shaft transmission units and three brakes A, B, D and the design ofthe main planetary gear set NS with two shiftable main planetarygearwheel assemblies NS1, NS2 coupled as two-web, four shafttransmission units and with two clutches M, H and a brake L, correspondsunchanged to that of the embodiment shown in FIG. 1A.

As shown in FIG. 2A, the spur gear arrangement ST still comprises spurgearwheel pairs ST11/ST12 and ST21/ST22. The spur gearwheel ST12 thatmeshes with ST11 can be connected to the solar gearwheel 31 of the firstmain planetary gearwheel assembly NS1 by means of the first shiftelement M of the main planetary gear set NS, which is formed as aclutch, and to the annular gearwheel 33 of the first main planetarygearwheel assembly NS1 and the web 45 of the second main planetarygearwheel assembly NS2 coupled to the annular gearwheel 33 by means ofthe second shift element H of the main planetary gear set, which is alsoformed as a clutch. The spur gearwheel ST22 that meshes with ST21 isconnected fast to the solar gearwheel 41 of the second main planetarygearwheel assembly NS2.

Owing to its very short axial extension, the second embodiment of amulti-stage gearbox is, according to the invention, in a particularlyadvantageous way, well suited for arrangements in motor vehicles havingthe drive motor positioned transversely to the driving direction withaxially restricted structural space for the gearbox.

As in the first embodiment of a multi-stage gearbox, according to theinvention described earlier, in the second embodiment the two spurgearwheel stages ST11/ST12 and ST21/ST22 of the spur gear arrangement STagain have transmission ratios of “one”. Obviously, in this case too,other transmission ratios can be provided, for example, in order toadapt the spur gearwheel diameter to an existing structural space. Thespur gearwheel stages ST11/ST12 and ST21/ST22 can also have differenttransmission ratios. In another design, it can be provided that thedriving and driven shafts of the spur gear arrangement ST are notaxis-parallel. In a further design, it can also be provided that the twospur gearwheel stages of the spur gear arrangement ST each have morethan two spur gearwheels or even a different number of spur gearwheelsin each spur gearwheel stage.

FIG. 3A now shows the transmission scheme of a third embodiment of amulti-stage gearbox according to the invention. In contrast to the firstand second embodiments described earlier, the reduction and mainplanetary gear sets VS and NS are this time connected to one another viaa bevel gearwheel stage KT instead of via the spur gearwheel stage ST.The respective central axes of the reduction and main planetary gearsets VS and NS are preferably at a right-angle to one another, so thatthe reduction and main planetary gear sets VS and NS are arranged nextto one another largely without spatial overlap.

The bevel gear arrangement KT, however, can also have some other anglebetween its driving and driven shafts. Besides, the bevel geararrangement KT can be made as a right-angle or non right-angle hypoidbevel gear arrangement with an axial offset, i.e., as a so-termed bevelworm gear.

The design of the reduction planetary gear set VS with two shiftablereduction planetary gearwheel assemblies VS1, VS2 coupled as two-web,four shaft transmission units and three brakes A, B, D and the design ofthe main planetary gear set NS with two shiftable main planetarygearwheel assemblies NS1, NS2 coupled as two-web, four shafttransmission units and with two clutches M, H and a brake L correspondsunchanged to that of the embodiments shown in FIGS. 1A and 2A.

As shown in FIG. 3A, the bevel gear arrangement KT comprises bevelgearwheel pairs KT11/KT12 and KT21/KT22. The bevel gearwheel KT12 thatmeshes with KT11 can be connected to the solar gearwheel 31 of the firstmain planetary gearwheel assembly NS1 by means of the first shiftelement M of the main planetary gear set NS, which is made as a clutch,and to the annular gearwheel 33 of the first main planetary gearwheelassembly NS1 and the web 45 of the second main planetary gearwheelassembly NS2 coupled to the annular gearwheel 33 by means of the secondshift element H of the main planetary gear set NS, also made as aclutch. The bevel gearwheel KT22 that meshes with KT21 is connected fastto the solar gearwheel 41 of the second main planetary gearwheelassembly NS2.

In the third example embodiment of a multi-stage gearbox according tothe invention shown in FIG. 3A, the two bevel gearwheel pairs KT11/KT12and KT21/KT22 are made with a transmission ratio of “one”. Obviously, inthis case too, other transmission ratios can be provided, for example,in order to adapt the bevel gearwheel diameter to an existing structuralspace. The bevel gearwheel pairs KT11/KT12 and KT21/KT22 can also havedifferent transmission ratios.

Owing to the angle between the reduction and main planetary gear sets,the third example embodiment of a multi-stage gearbox, according to theinvention, described is well suited for application in a motor vehicle,in a particularly advantageous way, with its drive motor arrangedlongitudinally relative to the driving direction (“front longitudinaldrive”, “rear longitudinal drive”), but also in motor vehicles withall-wheel drives.

In a further development of the invention (not illustrated here), it canalso be provided that the spur gear arrangement ST, according to theinvention, between the reduction and main planetary gear sets VS and NSis replaced by a chain drive. Between the connection shaft 2 and themain planetary gear set NS, and between the drive input shaft 1 and themain planetary gear set NS, in each case there are a driving and adriven wheel and in each case traction means, for example, a chain or atoothed belt, to transfer torque between the driving and the drivenwheel.

In principle, instead of the chain drive, which transfers torque in aform-enclosed way, a wrap-around drive can also be provided, whichtransfers torque by friction force, for example, via a V-belt.

In a design of the chain drive or wrap-around drive, only a single chainor a single wrap-around element can be provided, which is arrangedeither between the connection shaft 2 and the main planetary gear set NSor between the drive input shaft 1 and the main planetary gear set NS,while the respective other mechanical connection to the main planetarygear set NS is then formed as a single spur gear stage preferably withthree spur gearwheels.

REFERENCE NUMERALS

-   VS Reduction planetary gear set-   VS1 First reduction planetary gearwheel assembly-   VS2 Second reduction planetary gearwheel assembly-   NS Main planetary gear set-   NS1 First main planetary gearwheel assembly-   NS2 Second main planetary gearwheel assembly-   ST Spur gear arrangement-   ST11/ST12 First spur gearwheel stage between the drive input shaft    and the main planetary gear set-   ST21 /ST22 Second spur gearwheel stage between the connection shaft    and the main planetary gear set-   ST11 Input-side spur gearwheel of the first spur gear stage-   ST12 Output-side spur gearwheel of the first spur gear stage-   ST21 Input-side spur gearwheel of the second spur gear stage-   ST22 Output-side spur gearwheel of the second spur gear stage-   KT Bevel gear arrangement-   KT11/KT12 First bevel gearwheel stage between the drive input shaft    and the main planetary gear set-   KT21/KT22 Second bevel gearwheel stage between the connection shaft    and the main planetary gear set-   KT11 Input-side bevel gearwheel of the first bevel gear stage-   KT12 Output-side bevel gearwheel of the first bevel gear stage-   KT21 Input-side bevel gearwheel of the second bevel gear stage-   KT22 Output-side bevel gearwheel of the second bevel gear stage-   A, B, D First to third shift elements of the reduction planetary    gear set-   M, H, L First to third shift elements of the main planetary gear set-   n Input speed of the drive input shaft-   nvs Output speed of the reduction planetary gear set-   nns Output speed of the main planetary gear set-   1 Drive input shaft-   2 Output shaft of the reduction planetary gear set-   3 Drive output shaft-   11 Solar gearwheel of gearwheel assembly VS1-   12 Planetary gearwheel of gearwheel assembly VS1-   13 Annular gearwheel of gearwheel assembly VS1-   15 Web gearwheel of gearwheel assembly VS1-   21 Solar gearwheel of gearwheel assembly VS2-   22 Planetary gearwheel of gearwheel assembly VS2-   23 Annular gearwheel of gearwheel assembly VS2-   25 Web gearwheel of gearwheel assembly VS2-   31 Solar gearwheel of gearwheel assembly NS1-   32 Planetary gearwheel of gearwheel assembly NS1-   33 Annular gearwheel of gearwheel assembly NS1-   35 Web gearwheel of gearwheel assembly NS1-   41 Solar gearwheel of gearwheel assembly NS2-   42 Planetary gearwheel of gearwheel assembly NS2-   43 Annular gearwheel of gearwheel assembly NS2-   45 Web gearwheel of gearwheel assembly NS2

1. A multi-stage gearbox, with a drive input shaft (1) connected to areduction planetary gear set (VS), with a drive output shaft (3)arranged non-coaxially to the drive input shaft (1) and connected to amain planetary gear set (NS), with shift elements (A, B, D) that act onthe reduction planetary gearset (VS) and shift elements (M, H, L) thatact on the main planetary gear set (NS), such that by selectiveactuation of the shift elements (A, B, D, M, H, L) an input speed (n) ofthe drive input shaft (1) can be transferred for the engagement of atleast seven forward gears at the drive output shaft (3) in such mannerthat to shift from one gear to the next-higher or next-lower gear of theshift elements actuated at the time in each case only one shift elementis disengaged and one other shift element is engaged wherein thereduction planetary gear set (VS) comprises just one output shaft (2)rotating at an output speed (nvs) of the reduction planetary gear set(VS), the main planetary gear set (NS) can be connected to the driveinput shaft (1) by means of at least one second shift element (M, H)acting on the main planetary gear set (NS) via a first spur gearwheelstage (ST11/ST12) of a spur gear arrangement ST, and the main planetarygear set (NS) is connected to the output shaft (2) of the reductionplanetary gear set (VS) via a second spur gearwheel stage (ST21/ST22) ofthe spur gear arrangement (ST).
 2. The multi-stage gearbox according toclaim 1, wherein both spur gearwheel stages (ST11/ST12, ST21/ST22) ofthe spur gear arrangement (ST) have a transmission ratio of one.
 3. Themulti-stage gearbox according to claim 1, wherein both spur gearwheelstages (ST11/ST12, ST21/ST22) of the spur gear arrangement (ST) have atransmission ratio larger or smaller than one.
 4. The multi-stagegearbox according to claim 1, wherein the spur gearwheel stages(ST11/ST12, ST21/ST22) of the spur gear arrangement (ST) each have nonaxis-parallel driving and driven axles.
 5. The multi-stage gearboxaccording to claim 1, wherein the spur gearwheel stages (ST11/ST12,ST21/ST22) of the spur gear arrangement (ST) are each formed of a pairof spur gearwheels (ST11 and ST12, and ST21 and ST22), respectively. 6.The multi-stage gearbox according to claim 1, wherein the spur gearwheelstages (ST11/ST12, ST21/ST22) of the spur gear arrangement (ST) eachcomprise more then two spur gearwheels.
 7. The multi-stage gearboxaccording to claim 1, wherein the spur gearwheel stages (ST11/ST12,ST21/ST22) of the spur gear arrangement (ST) comprise a different numberof spur gearwheels.
 8. The multi-stage gearbox according to claim 1,whereir the reduction planetary gear se (VS) and the main planetarygearset (NS) are arranged axis-parallel substantially in one plane, andthe spur gear arrangement (ST) is arranged axially next to the reductionand main planetary gear sets (VS, NS) on the side thereof facing awayfrom a drive motor of the multi-stage gearbox.
 9. The multi-stagegearbox according to claim 1, wherein the reduction planetary gear set(VS) comprises at least two coupled, non-shiftable reduction planetarygearwheel assemblies (VS1, VS2), and the main planetary gear set (NS)comprises at least two coupled main planetary gearwheel assemblies (NS1,NS2), at least one of the main planetary gearwheel assemblies (NS1, NS2)being shiftable.
 10. The multi-stage gearbox according to claim 1,wherein the reduction planetary gear set (VS) comprises at least twocoupled reduction planetary gearwheel assemblies (VS1, VS2), at leastone of the said reduction planetary gearwheel assemblies (VS1, VS2)being shiftable, the main planetary gear set (NS) comprises at least twomain planetary gearwheel assemblies (NS1, NS2), at least one of the saidmain planetary gearwheel assemblies (NS1, NS2) being shiftable, and theoutput speed (nvs) of the reduction planetary gear set (VS) is producedby selective closing of the shift elements (A, B, D) acting on thereduction planetary gear set (VS).
 11. The multi-stage gearbox accordingto claim 9, wherein the output shaft (2) of the reduction planetary gearset (VS) is connected to a central gearwheel of the second mainplanetary gearwheel assembly (NS2) via the second spur gearwheel stage(ST21/ST22) of the spur gear assembly (NS2) via the second spurgearwheel stage (ST21/ST22) of the spur gear arrangement (ST) or thesecond bevel gear pair (KT21/KT22 of the bevel gear arrangement (KT).12. The multi-stage gearbox according to claim 9, wherein themulti-stage gearbox comprises two reduction planetary gearwheelassemblies (VS1, VS2), two main planetary gearwheel assemblies (NS1,NS2), and a total of six shift elements (A, B, D, M, H, L), and a totalof nine forward gears can be engaged.
 13. The multi-stage gearboxaccording to claim 10, wherein following features: the reductionplanetary gear set (VS) comprises three shift elements (A, B, D) and twocoupled, shiftable reduction planetary gearwheel assemblies (VSI, VS2),each with a solar gearwheel (11, 21), an annular gearwheel (13, 23) anda web (15, 25) with planetary gearwheels (12, 22); the main planetarygear set (NS) comprises three shift elements (H, M, L) and two coupled,shiftable main planetary gearwheel assemblies (NS1, NS2), each with asolar gearwheel (31, 41), an annular gearwheel (33, 43) and a web (35,45) with planetary gearwheels (32, 42); the spur or bevel geararrangement (ST or KT) comprises the first spur gearwheel stage(ST11/ST12) or the first bevel gearwheel stage (KT11/KT12) with a spuror bevel gearwheel (ST11 or KT11) on an input side and a spur or bevelgearwheel (ST12 or KT12) on an output side, and a second spur gearwheelstage (ST21/ST22) or a first bevel gearwheel stage (KT21/KT22) with aspur or bevel gearwheel (ST21 or KT21) on the input side and a spur orbevel gearwheel (ST22 or KT22) on the output side; the solar gearwheel(11) of the first reduction planetary gearwheel assembly (VS1) can befixed by means of the first shift element (A) of the reduction planetarygear set (VS); the solar gearwheel (21) of the second reductionplanetary gearwheel assembly (VS2) is connected to the drive input shaft(1); the annular gearwheel (13) of the first reduction planetarygearwheel assembly (VS1) and the web (25) of the second reductionplanetary gearwheel assembly (VS2) are connected to one another and canbe fixed by means of the third shift element (D) of the reductionplanetary gear set (VS); the annular gearwheel (23) of the secondreduction planetary gearwheel assembly (VS1) and the web (15) of thefirst reduction planetary gearwheel assembly (VS2) are connected to oneanother and to the output shaft (2) of the reduction planetary gear set(VS), and can be fixed by means of the second shift element (B) of thereduction planetary gear set (VS); the drive input shaft (1) isconnected to the spur or bevel gearwheel (ST11 or KT11) of the firstspur gear stage (ST11/ST12) or the first bevel gearwheel pair(KT11/KT12) on the input side; the output shaft (2) of the reductionplanetary gear set (VS) is connected to the spur or bevel gearwheel(ST21 or KT21) of the second spur gear stage (ST21/ST22) or the secondbevel gearwheel pair (KT21/KT22) on the input side; the solar gearwheel(31) of the first main planetary gearwheel assembly (NS1) can beconnected by means of the first shift element (M) of the main planetarygear set (NS) to the spur or bevel gearwheel (ST12 or KT12) of the firstspur gear stage (ST11/ST12) or the first bevel gear pair (KT11/KT12) onthe output side; the solar gearwheel (41) of the second main planetarygearwheel assembly (NS2) is connected to the spur or bevel gearwheel(ST22 or KT22) of the second spur gear stage (ST21/ST22) or the secondbevel gear pair (KT21/KT22 on the output side; the annular gearwheel(33) of the first main planetary gearwheel assembly (NS1) and the web(45) of the second main planetary gearwheel assembly (NS2) are connectedtogether, can be connected by means of the second shift element (H) ofthe main planetary gear set (NS) to the spur or bevel gearwheel (ST12 orKT12) of the first spur gear stage (ST11/ST12) or the first bevel gearpair (KT11/KT12) on the output side, and can be fixed by means of thethird shift element (L) of the main planetary gear set (NS); and theannular gearwheel (43) of the second main planetary gearwheel assembly(NS2) and the web (35) of the first main planetary gearwheel assembly(NS1) are connected together and to the drive output shaft (3).